1. Field of the Invention
The present invention relates to an airbag device for vehicles, and more particularly to an assembly structure of an airbag case wherein the edge of an airbag cover is hooked on a steering wheel, and a retainer is attached to a steering wheel core by means of bolts.
2. Description of the Related Art
Generally, an airbag device is a device mounted to a steering wheel of a vehicle for protecting a driver from injury when a collision of the vehicle occurs. Also, the airbag device is mounted to the steering wheel in such a manner that it is vertically moved, whereby the airbag device serves to turn on/off a horn switch mounted in the steering wheel.
FIG. 1 is a perspective view showing a conventional assembly structure of an airbag case, and FIG. 2 is a side view, in section, of the conventional assembly structure of the airbag case.
As shown in FIGS. 1 and 2, the conventional airbag device for vehicles comprises: an airbag case 10 to 13 mounted to a hub 2 of a steering wheel 1; an inflator 14 for supplying a high-pressure gas when a vehicle collision is detected by means of an impact sensor; and an airbag 16 expanding toward a passenger when the gas is supplied from the inflator 14 to the airbag 16.
The hub 2 of the steering wheel 1 is formed in such a manner that the width of the hub 2 is gradually increased from the lower part thereof to the upper part thereof. The hub 2 has an open top part and a bottom part, through which a hub hole 2A is formed. Inside the hub 2 is mounted a steering wheel core 4, which is extended to a rim 3 of the steering wheel 1.
The airbag case 10 to 13 comprises: an airbag cover 10 for covering the open top part of the hub 2 of the steering wheel 1; a retainer 11 disposed on the steering wheel core 4 for retaining the inflator 14 and the airbag 16; a rib 12 protruded from the airbag cover 10 in such a manner that the rib 12 surrounds the retainer 11, the rib 12 being attached to the retainer 11 by means of rivets 20; and brackets 13 attached to the rib 12 and the retainer 11 by means of the rivets 20 and attached to the steering wheel core 4 by means of bolts 22.
At the airbag cover 10 is formed a tear line 17. More specifically, the tear line 17 is formed at the rib-inside area 10A of the airbag cover 10, which is placed inside the rib 12. Consequently, the airbag cover 10 is severed along the tear line 17 when the airbag 16 is expanded.
The retainer 11 is mounted coaxially with the airbag cover 10. In other words, the retainer 11 and the airbag cover have the same central axis C. The width 11W of the retainer 11 is approximately ½ of the width 10W of the airbag cover 20. The rib 12 is formed halfway between the central axis C and the edge of the airbag cover 10 so that the rib 12 comes in contact with a sidewall 11A of the retainer 11. Consequently, the rib-inside area 10A of the airbag cover 10, which is placed inside the rib 12, corresponds exactly to the area where the tear line is formed. In other words, the area of the airbag cover 10 within the tear line 17 is approximately ½ of the area of the entire airbag cover 10.
The operation of the conventional assembly structure of the airbag case with the above-stated construction will now be described.
When a vehicle collision is detected by means of the impact sensor, the high-pressure gas is supplied from the inflator 14 to the airbag 16. As the gas is filled in the airbag 16, the airbag 16 is expanded so that the airbag cover 10 is severed along the tear line 17, and is then fully expanded toward a passenger.
In the conventional assembly structure of the airbag case, the shape of the tear line 17 is experimentally designed since the expansion performance of the airbag 16 is affected by the shape of the tear line 17. However, the area of the airbag cover 12 within the tear line 17 is limited to approximately ½ of the area of the entire airbag cover 10 due to the rib 12. Consequently, the expansion performance of the airbag 16 may be improved only restrictively.
To the airbag cover 10 is mounted a membrane type horn switch 18, by which a horn sounding an alarm is operated. The horn switch 18 is disposed inside the rib 12 so that interference between the horn switch 18 and the rib 12 is prevented. As a result, an area in which the horn switch 18 can be disposed and operated is limited.
The conventional assembly structure of the airbag case provides no additional supporting member for supporting the edge of the airbag cover 10. As a result, the edge of the airbag cover 10 is loosened from the steering wheel 1, which leads to poor appearance. The rib 12 is formed at a distance from the edge of the airbag cover 10, and therefore the edge of the airbag cover 10 in not securely and reliably supported by the rib 12.
In the conventional assembly structure of the airbag case, the rib 12, the retainer 11, and the brackets 13 are fastened together by means of the rivets 20, and then the brackets 13 are attached to the steering wheel core 4 by means of the bolts 22. In this way, the airbag case 10 to 13 is assembled with the steering wheel 1, whereby the number of the parts to be assembled is large, additional tools for rivet 20 and bolt 22 works are required, and thus the cost and time of assembly are increased.